At the present time, there is an increased need for torque monitoring on rotating shafts in vehicles where improved operation is needed. It is desirable to measure torque for power train and drive line, and then include the sensing result in a closed loop operation for smooth, reliable operation and lower fuel use. In addition, torque monitoring can be of tremendous importance for the structural health monitoring (SHM) of different civil infrastructures and assets such as buildings, bridges, pumps and the like.
Real time monitoring and predictive condition based maintenance practices are another place where torque sensors can be of value. The measurement of torque on moving parts of an engine is, of course, the most challenging process, and involves wireless sensing and detector capability to withstand the automotive industry specifications of a much higher temperature and significant vibration. In the automotive domain, specific materials for sensor realization and the related attachment technology are the key features that need to be addressed. Wireless optical and magnetic principles are frequently used, but the main disadvantages for these remains the high costs of such sensors and the quality of attachment technology specific to the harsh environmental conditions.
In the past two decades, surface acoustic wave (SAW) technology devices have been tried for such torque applications, due to their advantages of passive and wireless operation capabilities in conjunction with low cost that is specific to integrated circuit (IC) like technology for SAW torque sensor fabrication. The SAW sensor is a strain sensitive device and can be wirelessly interrogated from a distance for giving torque information from the position where it is located.
In the prior art, different SAW packaging solutions and attachment technologies have been tried, but they are not passing either the low cost requirement or functional requirement in term of low stress introduced by the package, primarily the technology used to attach the sensor. The strain transmission with high fidelity from the rotating shaft to the sensor is another prerequisite that has not been met. Prior art technologies for SAW packaging and attachment to the substrate have suffered from being labor cost intensive.
Accordingly, one advantage of the present invention is to provide a visionary, low cost and flexible technology that is industrially applicable for SAW torque packaging and attachment to a shaft.
Another advantage of the present invention is to provide a technology that considers the specific requirements of each type of shaft and allow a robust sensor operation in the harsh environment of the automotive industry.
Yet another advantage of this invention is that this technology will be based in IC technology extension at the lever of sensor packaging in terms of wafer level packaging and the use of low cost materials for a package that can be fitted with a piezoelectric substrate in terms of similar thermal expansion coefficients.
Other advantages will appear hereinafter.